Michael Obland

Power subsystem design for the Montana EaRth Orbiting Pico-Explorer (MEROPE) CubeSat-class satellite

Montana State Universitys Space Science and Engineering Laboratory (SSEL) under support from the Montana NASA Space Grant Consortium is engaged in an Earth orbiting satellite student project that will carry a reproduction, using current-day technology, of the scientific payload flown on Explorer-1 in 1958 into a 650 km sun-synchronous polar orbit. The off-the-shelf emphasis of the MEROPE component selections has required the power system to adapt to widely different electrical needs across subsystems. The size limitations of the CubeSat-class specifications confine body-mounted solar arrays to approximately 64 cm/sup 2/ per side, restricting overall power production and necessitating the use of an extremely efficient power bus. MEROPE will employ dual junction GaAs solar cells (19% efficiency) to produce the 5 W necessary for satellite operation and battery maintenance. Included in the system will be two Li-ion battery cells chosen for their high energy density, rapid charge characteristics, low mass, and lack of memory effects. The power system is responsible for providing a highly regulated 5 V bus to the microcontroller subsystem and a 6 V bus to the communication subsystem. In addition, the Geiger tube scientific payload aboard MEROPE requires a stable 500 V high voltage power supply (HVPS) to operate the experiment. This will be accomplished using a prototype HVPS requiring +/- 5 V buses.

Microcontroller design for the Montana EaRth Orbiting Pico-Explorer (MEROPE) Cubesat-class satellite

Montana State Universitys Space Science and Engineering Laboratory (SSEL) under support from the Montana NASA Space Grant Consortium is engaged in an Earth orbiting satellite student project that will carry a reproduction, using current-day technology, of the scientific payload flown on Explorer-1 in 1958 into a 650 km sun-synchronous polar orbit. On-board operations will be commanded by a Motorola MC68HC812A4 (HC12) microcontroller, chosen for its ease of use, processing power, and intrinsic features. Accompanying this will be an Integrated Device Technology CMOS Supersync First-in, First-Out (FIFO) IDT72291 150 Kbyte RAM chip, used for storing scientific data and system telemetry before downlink to ground station. The RAM was selected for the simplicity of the FIFO data flow. The HC12 is responsible for controlling antenna deployment, communication handling, and other system parameters. System interrupts allow the HC12 to seamlessly collect payload data, attitude data, battery conditions (voltage, current, charge state, and temperature), bus voltage, bus current, processor temperature, and stability of the payload high voltage power supply. This paper describes MEROPEs computer subsystems in detail.

Diode laser transmitter for water vapor DIAL measurements

The design and performance of two diode laser based transmitters for differential absorption LIDAR (DIAL) are presented. The first laser transmitter uses a tunable external cavity diode laser (ECDL) in the Littman-Metcalf cavity configuration to injection seed a flared amplifier. Water vapor absorption measurements are demonstrated with this laser transmitter operating in a continuous wave mode. The second diode based laser transmitter uses an ECDL in the Littrow cavity configuration and angle-angle semiconductor optical amplifiers to produce amplified laser pulses. Both designs are easily adaptable to wavelengths in the visible to the near infrared spectral region.

Progress toward a water-vapor differential absorption lidar (DIAL) using a widely tunable amplified diode laser source

Water vapor is one of the most significant constituents of the atmosphere because of its role in cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Some details of the role of water vapor and related feedback mechanisms in the Earth system need to be characterized better if local weather, global climate, and the water cycle are to be understood. A Differential Absorption LIDAR (DIAL) with a compact laser diode source may be able to provide boundary-layer water vapor profiles with improved vertical resolution relative to passive remote sensors. While the tradeoff with small DIAL systems is lower vertical resolution relative to large LIDARs, the advantage is that DIAL systems can be built much smaller and more robust at less cost, and consequently are the more ideal choice for creating a multi-point array or satellite-borne system. This paper highlights the progress made at Montana State University towards a water vapor DIAL using a widely tunable amplified external cavity diode laser (ECDL) transmitter. The ECDL is configured in a Littman-Metcalf configuration and was built at Montana State University. It has a continuous wave (cw) output power of 20 mW, a center wavelength of 832 nm, a coarse tuning range of 17 nm, and a continuous tuning range greater than 20 GHz. The ECDL is used to injection seed a tapered amplifier with a cw output power of 500 mW. The spectral characteristics of the ECDL are transferred to the output of the tapered amplifier. The rest of the LIDAR uses commercially available telescopes, filter optics, and detectors. Initial cw and pulsed absorption measurements are presented.

Development of a widely tunable amplified diode laser differential absorption lidar for profiling atmospheric water vapor

This work describes the design and testing of a highly-tunable differential absorption lidar (DIAL) instrument utilizing an all-semiconductor transmitter. This new DIAL instrument transmitter has a highly-tunable external cavity diode laser (ECDL) as a seed laser source for two cascaded commercial tapered amplifiers. The transmitter has the capability of tuning over a range of ~ 17 nm centered at about 832 nm to selectively probe several water vapor absorption lines. This capability has been requested in other recent DIAL experiments for wavelengths near 830 nm. The transmitter produces pulse energies of approximately 0.25 μJ at a repetition rate of 20 kHz. The linewidth is exceptionally narrow at <0.3 MHz, with frequency stability that has been shown to be +/- 88 MHz and spectral purity of 0.995. Tests of the DIAL instrument to prove the validity of its measurements were undertaken. Preliminary water vapor profiles, taken in Bozeman, Montana, agree to within 5-60% with profiles derived from co-located radiosondes 800 meters above ground altitude. Below 800 meters, the measurements are biased low due to a number of systematic issues that are discussed. The long averaging times required by low-power systems have been shown to lead to biases in data, and indeed, our results showed strong disagreements on nights when the atmosphere was changing rapidly, such as on windy nights or when a storm system was entering the area. Improvements to the system to correct the major systematic biases are described.

Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements

Recent advances using electronic feedback to control the op- tical cavity length of external cavity diode lasers ECDLs have led to extended continuous tuning ranges. Mode-hop-free tuning over more than 65 GHz has been demonstrated. The ability to tune ECDLs asross a wide range is particularly useful to differential absorption lidar DIAL systems that use ECDLs as seed laser sources. Experiments using a multiple-pass gas absorption cell are performed to test a widely tunable, amplified ECDL DIAL transmitter with this extended tuning range system. Experimental results show that the system can be tuned to and main- tained at a user-defined wavelength for one hour, then tuned to and maintained at a second user-defined wavelength for one hour without mode hopping. This tuning is successfully accomplished between wave- lengths separated by approximately 44 GHz. A computer-controlled feedback loop in the tuning system tunes and holds the laser system to the on- and off-line wavelengths to within ±88 MHz. The laser power transmitted through the gas absorption cell is monitored and used to perform a differential absorption calculation to find the number density of water vapor molecules within the cell. The measured value is in agree- ment with a HiTRAN prediction of the expected value.

Preliminary Testing of a Water-Vapor Differential Absorption LIDAR (DIAL) Using a Widely Tunable Amplified Diode Laser Source

Water vapor plays an enormous role in Earths atmospheric dynamics through cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Detailed data of water vapor distribution and flux and related feedback mechanisms are required to better understand and predict local weather, global climate, and the water cycle. One method of obtaining this data in the boundary layer with improved vertical resolution relative to passive remote sensors is with a Differential Absorption LIDAR (DIAL) utilizing a compact laser diode source. While small, low power DIAL systems do not typically have the resolution capabilities of larger LIDARs, DIAL systems can be built much smaller and more robust at less cost, and therefore may be a reasonable choice for a multi-point array or satellite-borne system. Montana State University, with the expertise of its laser source development group, is engaged in experiments leading to a water vapor DIAL system that utilizes a widely tunable amplified external cavity diode laser (ECDL) transmitter. This transmitter will have the ability to tune across a 17 nm spectrum near 830 nm, allowing it access to multiple water vapor absorption lines of varying strengths. Because of this wide tunability, the optimal absorption line for the DIAL technique in this region can be used based upon existing atmospheric conditions. This paper highlights the progress made in several areas at Montana State University (MSU) towards characterization, design, and construction of a water vapor DIAL using this widely tunable amplified ECDL transmitter.

Initial results from a water vapor differential absorption lidar (DIAL) using a widely tunable amplified diode laser source

It is widely agreed that water vapor is one of the most important gasses in the atmosphere with regards to its role in local weather, global climate, and the water cycle. Especially with the growing concern for understanding and predicting global climate change, detailed data of water vapor distribution and flux and related feedback mechanisms in the lowest 3 km of the troposphere, where most of the atmospheric water vapor resides, are required to aid in climate models. Improved capabilities to monitor range-resolved tropospheric water vapor profiles continuously in time at many locations are needed. One method of obtaining this data in the boundary layer with improved vertical resolution relative to passive remote sensors is with a Differential Absorption LIDAR (DIAL) utilizing a compact laser diode source. Montana State University, with the expertise of its laser source development group, has developed a compact water vapor DIAL system that utilizes a widely tunable amplified external cavity diode laser (ECDL) transmitter. This transmitter has the ability to tune across a 17 nm spectrum near 830 nm, allowing it access to multiple water vapor absorption lines of varying strengths. A novel tuning system tunes and holds the ECDL to within +/- 88 MHz (0.20 pm) of the selected wavelength. The ECDL acts as a seed source for two commercial cascaded tapered amplifiers. The receiver uses commercially available optics and a fiber-coupled Avalanche Photodiode (APD) detector. Initial nighttime measurements of water vapor profiles taken over Bozeman, Montana, with comparisons to radiosonde-derived profiles will be presented.

Advancements towards active remote sensing of CO2 from space using intensity-modulated, continuous-Wave (IM-CW) lidar

The Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) CarbonHawk Experiment Simulator (ACES) is a NASA Langley Research Center instrument funded by NASA’s Science Mission Directorate that seeks to advance technologies critical to measuring atmospheric column carbon dioxide (CO2) mixing ratios in support of the NASA ASCENDS mission. The ACES instrument, an Intensity-Modulated Continuous-Wave (IM-CW) lidar, was designed for high-altitude aircraft operations and can be directly applied to space instrumentation to meet the ASCENDS mission requirements. Airborne flight campaigns have been used to demonstrate ACES’ advanced technologies critical for a spaceborne instrument with lower platform consumption of size, mass, and power, and with improved performance. ACES recently flew on the NASA DC-8 aircraft during the 2017 NASA ASCENDS/Arctic-Boreal Vulnerability Experiment (ABoVE) airborne measurement campaign to test ASCENDS-related technologies in the challenging Arctic environment. Data were collected over a wide variety of surface reflectivities, terrain, and atmospheric conditions during the campaign’s eight research flights. ACES also flew during the 2017 and 2018 Atmospheric Carbon and Transport – America (ACT-America) Earth Venture Suborbital - 2 (EVS-2) campaigns along with the primary ACT-America CO2 lidar, Harris Corporation’s Multi-Frequency Fiber Laser Lidar (MFLL). Regional CO2 distributions of the lower atmosphere were observed from the C-130 aircraft during the ACT-America campaigns in support of ACT-America’s science objectives. The airborne lidars provide unique remote data that complement data from more traditional in situ sensors. This presentation shows the applications of CO2 lidars in meeting these science needs from airborne platforms and an eventual spacecraft.